The subject matter of this invention relates generally to circuit breakers with fault detecting systems and more particularly to circuit breakers which can distinguish between three-phase and single-phase faults. Electronically controlled circuit breakers which are capable of being actuated on the occurrence of predetermined amount of fault current in the line to be protected are well known in the prior art. Such a circuit breaker is described in U.S. Pat. No. 3,818,275, issued June 18, 1974, to A. B. Shimp and assigned to the assignee of the present invention. Circuit breakers of this kind enjoy wide and diverse use in industry. Some of these circuit breakers are employed in the underground mining industry, for example. However, in the mining industry, mobile machinery, such as shuttle cars, continuous mining machines, etc., are electrically powered by way of trailing cables. Limits on the maximum allowable trip settings of the circuit breakers protecting these cables are specified by government regulations in many cases. Often the maximum allowable setting for a particular size cable is so low as to allow nuisance tripping of the circuit breaker when large motors on the mounting machines are started or stalled. It would be advantageous if circuit breaker systems could be devised in which the government's maximums could be adhered to without introducing undesirous nuisance tripping.